/* Copyright (c) 2020 XEPIC Corporation Limited */
#ifndef IVL_StringHeap_H
#define IVL_StringHeap_H
/*
 * Copyright (c) 2002-2014 Stephen Williams (steve@icarus.com)
 *
 *    This source code is free software; you can redistribute it
 *    and/or modify it in source code form under the terms of the GNU
 *    General Public License as published by the Free Software
 *    Foundation; either version 2 of the License, or (at your option)
 *    any later version.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU General Public License for more details.
 *
 *    You should have received a copy of the GNU General Public License
 *    along with this program; if not, write to the Free Software
 *    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
 * USA.
 */

#include <string>

using namespace std;

class perm_string {
 public:
  perm_string() : text_(0) {}
  perm_string(const perm_string& that) : text_(that.text_) {}
  ~perm_string() {}

  inline bool nil() const { return text_ == 0; }

  perm_string& operator=(const perm_string& that) {
    text_ = that.text_;
    return *this;
  }

  const char* str() const { return text_; }
  operator const char*() const { return str(); }

  // This is an escape for making perm_string objects out of
  // literals. For example, perm_string::literal("Label"); Please
  // do *not* cheat and pass arbitrary const char* items here.
  static perm_string literal(const char* t) { return perm_string(t); }

 private:
  friend class StringHeap;
  friend class StringHeapLex;
  explicit perm_string(const char* t) : text_(t){};

 private:
  const char* text_;
};

extern const perm_string empty_perm_string;
extern bool operator==(perm_string a, perm_string b);
extern bool operator==(perm_string a, const char* b);
extern bool operator!=(perm_string a, perm_string b);
extern bool operator!=(perm_string a, const char* b);
extern bool operator>(perm_string a, perm_string b);
extern bool operator<(perm_string a, perm_string b);
extern bool operator>=(perm_string a, perm_string b);
extern bool operator<=(perm_string a, perm_string b);
extern ostream& operator<<(ostream& out, perm_string that);

/*
 * The string heap is a way to permanently allocate strings
 * efficiently. They only take up the space of the string characters
 * and the terminating nul, there is no malloc overhead.
 */
class StringHeap {
 public:
  StringHeap();
  ~StringHeap();

  const char* add(const char*);
  perm_string make(const char*);

 private:
  char* cell_base_;
  unsigned cell_ptr_;

 private:  // not implemented
  StringHeap(const StringHeap&);
  StringHeap& operator=(const StringHeap&);
};

/*
 * A lexical string heap is a string heap that makes an effort to
 * return the same pointer for identical strings. This saves further
 * space by not allocating duplicate strings, so in a system with lots
 * of identifiers, this can theoretically save more space.
 */
class StringHeapLex : private StringHeap {
 public:
  StringHeapLex();
  ~StringHeapLex();

  const char* add(const char*);
  perm_string make(const char*);
  perm_string make(const string&);

  unsigned add_count() const;
  unsigned add_hit_count() const;
  void cleanup();

 private:
  enum { HASH_SIZE = 4096 };
  const char* hash_table_[HASH_SIZE];

  unsigned add_count_;
  unsigned hit_count_;

 private:  // not implemented
  StringHeapLex(const StringHeapLex&);
  StringHeapLex& operator=(const StringHeapLex&);
};

#endif /* IVL_StringHeap_H */
